The electric field-induced luminescence is also known as Electroluminescence (EL). In 1936, a French scientist G. Destriau discovered this phenomenon for the first time, so it is an 80 years old technology. Destriau found that a powdered fluorescent material when immersed in liquid dielectric material can generate continuous bright light under the application of an alternating electric field. But, in the following 10 years, this phenomenon did not attract much attention. Its significance was doubted and it was hard to realize its potential applications.
Subsequently, Destriau designed and fabricated some other planar EL devices. However, it was not until 1947, when conductive glass was invented, was a research and development boom set off using conductive glass as transparent electrodes for EL devices.
Nevertheless, after another 10 years, limitations on the brightness, life-time and light color of alternating current electroluminescent devices (referred to as ACEL) became evident and people's enthusiasm about EL devices began to subside. Almost at the same time, direct current electroluminescent devices (referred to as DCEL) began to be developed rapidly. In 1971, Chinese researchers found that ZnS: Mn/Cu had better light emitting characteristics under AC voltage compared to DC voltage. This is the only available EL material, so far, that can work with both AC and DC (referred to as ADCEL).
Although EL research continues until today, it is mainly based on display illumination. Moreover, these EL devices having vertical structure with top and bottom electrodes present serious problems like: (1) such structure can only be used for display lighting and cannot meet more diverse needs and uses; (2) since both top and bottom electrodes are required, the production process is more complex and production cost is higher; (3) the structure requires one transparent electrode. If the bottom electrode is transparent, it also requires a transparent substrate, thereby restricting the choice of substrate material.
A number of planar electroluminescent devices are based on inorganic electroluminescent materials. Compared to inorganic electroluminescent material, organic light-emitting materials have low driving voltage, efficient luminescence, abundant color, simple fabrication, low cost, wide selection of materials and so on. Currently, with the increasing development of information technology, people put forward higher requirements on information display technology. Display with abundant color, low energy, environmental protecting, lightweight and even flexible become what people pursue. Compared with other display technology, organic electroluminescence has many superiorities, which just meet the demands of the time. Organic light-emitting devices as an emerging research field constantly attracts more and more people's attention, and it may become a kind of ideal display technology in the information age.
In summary, there is a need for planar EL devices with improved structural arrangements.